Integrated circuits are typically fabricated on a substrate, which is subsequently singulated to produce the individual integrated circuits. As the term is used herein, “integrated circuit” includes devices such as those formed on monolithic semiconducting substrates, such as those formed of group IV materials like silicon or germanium, or group III-V compounds like gallium arsenide, or mixtures of such materials. The term includes all types of devices formed, such as memory and logic, and all designs of such devices, such as MOS and bipolar. The term also comprehends applications such as flat panel displays, solar cells, and charge coupled devices.
Before singulation, the integrated circuits on the substrate are processed through a number of different steps. Many of these process steps, and many of the transfer operations between the process steps, use so-called wafer chucks to retain, move, and position the substrates. For example, a chuck is used to retain and spin the substrate during a photoresist coating operation. Chucks are also used to retain and heat or cool a substrate during a sputter deposition process.
Chucks operate by having some retaining means that holds the substrate, with the back of the substrate in physical contact with the face of the chuck. The retaining means take on different forms, such as clamps against the face of the substrate that retain the substrate against the face of the chuck, annular vacuum rings that draw the back of the substrate against the face of the chuck, and alternating electrostatic charges that hold the substrate against the face of the chuck. In each instance, however, the back of the substrate is in physical contact with the face of the chuck. This physical contact has the tendency to introduce physical damage in and contamination to the substrate.
What is needed, therefore, is a system that overcomes problems such as those described above, at least in part.